1. Field of the Invention
The invention relates to a zoom lens and an optical imaging device including the same.
2. Description of the Related Art
Digital still cameras (DSCs) including a solid state imaging device such as a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS), or digital video cameras (DVCs) are widely used. In particular, demands for camera modules with mega-pixel resolution have increased, and cameras having picture resolution higher than 5 million pixels are frequently employed. Optical imaging devices such as digital still cameras (DSCs) using a CCD or a CMOS, or mobile phone cameras are required to have small size, light weight, and low manufacturing costs.
In order to meet the demands for camera miniaturization, when photographing is performed, a lens is extended from or retracted into a main camera body in a predetermined position, and when photographing is not performed, a collapsible lens barrel that is accommodated in the camera and is driven to arrange lenses along an optical axis has been widely used. In such a collapsible camera, when the collapsible lens barrel is accommodated in the camera, a distance between lens groups must be minimized so that the thickness of a camera can be decreased and portability of the camera can be improved. In the collapsible lens barrel, the number of lens groups must be decreased in order to manufacture a small-sized and thin camera. In this case, excellent picture resolution needs to be ensured.
In order to satisfy these demands, a conventional zoom lens including three lens groups has been widely used. Also, a conventional zoom lens system including a small-sized photographing lens system having 2× zoom ratio has been introduced. In the conventional zoom lens including three lens groups, the first lens group has a negative refractive power, the second lens group has a positive refractive power as a whole, and the third lens group has a positive refractive power, and the three lens groups are sequentially arranged from an object side to an image side of the conventional zoom lens. However, with such a conventional lens it is difficult to satisfy the demands for miniaturization and low lens manufacturing costs and also achieve a high zooming rate.